When a conventional ultrasonic inspection method is applied to a nuclear reactor piping system as shown in FIG. 15, the following two problems occur.
1) As shown in FIG. 15, a reactor container contains pipes of a primary piping system, and a turbine building contains pipes of a secondary piping system. As shown here, many reactor pipes are installed in both piping systems, and the total length thereof is gigantic.
The conventional ultrasonic inspection method, which is performed by repeating inspections at local sites, has a problem that a huge number of steps of the inspection work is necessary.
2) With the conventional ultrasonic inspection method, the technological determination criteria required for analysis vary depending on the person who performs measurement and analysis. Therefore, the conventional ultrasonic inspection method has a problem that an error may occur in the evaluation on the development of a tiny flaw caused by an over-time change thereof.
In order to solve the problems (1) and (2), the present applicant has already filed a patent application on an invention relating to “Ultrasonic inspection method and apparatus utilizing resonance phenomenon” (PCT/JP2004/16982).
The prior invention made by the present application relates to an ultrasonic inspection method for extracting a narrowband component wave from a wideband received wave with frequencies n·f1 and n·fs1 (n is an integer of 1 or greater) using resonance frequencies f1=VP/2W and fs1=γ1·f1 (γ1 is a sonic speed ratio of transverse wave and longitudinal wave).
Specifically, in order to inspect presence/absence of a flaw in a thickness immediately below a line segment connecting a pair of probes distanced by an interval of “a”, which are a transmission probe and a reception probe, the following is performed. Using one method of moving the probes, the pair of probes are moved by a defined distance in a direction perpendicular to the line segment connecting the pair of probes while the interval between the pair of probes is maintained. Each time when the probes are thus moved, a wideband ultrasonic wave is input from the transmission probe and a wideband ultrasonic wave is received by the reception probe. Based on the wideband received waves Gj(t) (j is the measurement point number) obtained at many measurement points, narrowband component waves GAj(t) are extracted with a sizing coefficient ns4 at the frequencies n·f1 and n·fS1. A comparative display of the component waves GAj(t) is presented with the sizing coefficient ns1, ns2 and ns3. Based on the generation state of the component waves GAj(t) thus displayed in comparison, the presence/absence of a flaw immediately below the line segment connecting the pair of probes is inspected for each j.
According to the prior invention made by the present applicant, the transmission probe and the reception probe are translated by a predetermined distance in a direction perpendicular to the line segment connecting the centers of the probes, so that flaws in an inspection target immediately below the line segment can be inspected all at once. Therefore, as compared with the conventional ultrasonic inspection method, the number of measurement points can be reduced to one several tenth or even to one several hundredth and thus the number of steps of the inspectionwork can be significantly reduced. This can contribute to the solution of the problem (1) above.
However, the above-described ultrasonic inspection method still has the following problem.
3) Due to the variety of locations and manners of movement of the probes, the method still has difficulties in terms of automatic measurement.
According to the prior invention made by the present applicant, even where different operators perform the measurements, as long as the analysis is performed with the same conditions of the sizing coefficients used for realizing higher precision of the inspection, the difference in the sizing result caused due to the varying capability of the measuring operators can be eliminated. Therefore, an accurate evaluation on the development of a tiny flaw caused by an over-time change thereof is made possible. This can contribute to the solution of the problem (2) above.
However, even with the above-described ultrasonic inspection method, there is still the following problem.
4) As a premise of the evaluation, the required received wave Gj(t) needs to be obtained at exactly the same position as in the immediately previous measurement. However, due to the variety of locations and manners of movement of the probes at the time of the measurement, it is difficult to locate and move the probes in the same manner as in the immediately previous measurement.